Employing media richness theory, a model is developed to open the black box surrounding the impact of computer-mediated communication systems on decision quality. The effects on decision quality of two important communication system factors, cue multiplicity and feedback immediacy, are examined in light of three important mediating constructs: social perceptions, message clarity, and ability to evaluate others, A laboratory experiment examining two tasks and employing face-to-face, electronic meeting, electronic conferencing, and electronic mail communication systems is used to assess the model's validity. Results provide consistent support for the research model as well as media richness theory. Richer media facilitate social perceptions (total socio-emotional communication and positive socio-emotional climate) and perceived ability to evaluate others' deception and expertise. Leaner media (electronic mail and electronic conferencing) facilitate communication clarity when participants have less task-relevant knowledge. The impacts of these mediating constructs on decision quality were found to depend on the levels of participant expertise and deception. In general, it was found that richer media can have significantly positive impacts on decision quality when participants' task-relevant knowledge is high. Moreover, effects of participant deception can be mitigated by employing richer media.